Draft gear



E. H. HARTEL 3,462,024

DRAFT GEAR I ,2 Sheets-Sheet 1 I Aug. 19, 1969 v Filed Kay 16. 1967INVENTOR ERW/N H. HARTEL A'IT EY mm mu wN On mm THHMHMMHHWTH M UnitedStates Patent US. Cl. 213-8 12 Claims ABSTRACT OF THE DISCLOSURE A draftgear in the form of a hydropneumatic shock absorber providing end-of-carcushioning in draft as well as in buff. The gear dissipates energythrough dynamic damping during bufi action by forcing oil at highvelocity through a continuously varying orifice, and an air chargeprovides a preload in both directions and serves also to return the unitto neutral after a stroke in either direction. During such return, theoil flows oppositely to the flow during buff at a valve controlled rateto prevent sudden extension. A special relief-valve arrangement affordsoverload protection in the event of harder than normal impact duringbuff.

This invention relates to hydropneumatic draft gear for railroad cars.

It is a primary object of the invention to provide an improved gear forhydropneumatic cushioning at high efficiency in a unit that will fit thestandard freight car draft gear pocket. Another object is to providesuch draft gear which is fully hydropneumatic, to the exclusion ofmechanical springs and thus distinguishable from known impact energyabsorbing mechanisms for railway vehicles in which such springs areemployed in conjunction with liquid cushioning means.

It is another object to provide such hydropneumatic end-of-carcushioning in both buff and draft, thereby greatly to minimize problemsof train dynamics.

It is an additional object to provide such draft gear in which theenergy of impact is dissipated by forcing of the oil at high velocitythrough a continuously varying orifice against an air spring, with valvecontrol of the flow of oil in the opposite direction providing apredetermined snubbing action in the return of the unit to the neutralposition after the impact has been absorbed and in the operation of thegear in draft. Rapid extension if the unit is thus prevented in theseconditions which might produce unwanted reaction forces on the car. Suchoperating mode in draft provides virtually solid-train operation,thereby minimizing the increase in train length which has beenexperienced and found objectionable in many conventional end-of-carcushioning devices.

Another object is to provide such hydropneumatic draft gear includingimproved relief valve protection against overload, for example, in theevent of greater than normal impact.

It is also an object of the present invention to provide such draft gearin a simple and self-contained design of high structural integrity andrequiring no external connections or accessories.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however,

3,462,024 Patented Aug. 19, 1969 of but a few of the various ways inwhich the principle of the invention may be employed.

In said annexed drawings:

FIGS. 1 and la are longitudinal sections which together show a fulldraft gear in accordance with the present invention:

FIG. 2 is a transverse cross-sectional view of the plane of which isshown by the line 22 in FIG. 1; and

FIG. 3 is a further transverse section as viewed from the plane of theline 3-3.

Referring now to the drawings in detail, the illustrative embodiment ofthe invention is a gear basically comprising a coupler head section 10,which can be of any known type, a cylinder 11 welded to and extendingfrom the coupler head, a hollow piston 12 within and projecting from thecylinder, and a piston fitting or cap 13.

The fitting 13 is a forging or casting welded to the outer end of thehollow piston and having a cavity 14 which complements the latter in thesense of forming a closed and extension of the piston interior. Thisfitting is further formed with a horizontal lug 15 in which there is avertical aperture 16 for pin connection of the gear to the railway car.The dashed outline 17 represents a standard freight car sill, and itwill be appreciated that the gear is simply inserted in such a sill andsupported in any suitable manner. A solid plate, such as shown by thefurther dashed outline 18, which closes the sill bottom over the fulllength of the gear is recommended to protect the piston in particularfrom direct impingement of debris, and it is also preferred thatantiturn blocks 19, 20 and 21 be secured to the exterior of the cylinderto prevent rotation of the coupler. The bottom block 19 engages thehanger plate, while the other blocks 20 and 21 are separate angularprojections respectively adjacent the upper corners of the sill.

A piston head 22 is threaded on the inner end of the hollow piston 12and locked by one or more dowel pins 23 which extend radially throughthe internally threaded skirt part 24 of the piston head and into thepiston. The periphery of this portion 24 is relieved by a multiplicityof circumferentially spaced axial slots 25, cooperably with the innersurface of the cylinder 11, and also a clear annular space 26 at theouter side of such slotted part. A ring valve 27 in the form of a splitring of significant axial extent and having a series of spaced aperturesor orifices 28 encircles the portion of the piston head at the annularspace 26 and communication from the latter to the interior of the pistonis provided by a series of radial passages 29 through this portion ofthe head.

The piston head is supported for relative movement in the cylinder by asplit bronze ring bearing 30 seated partially in a peripheral groove inthe piston head, and a central metering orifice 31 is provided in thepiston head for fiow of hydraulic fluid from the cylinder to theinterior of the piston. This flow is programmed by a metering pin 32which extends from a secondary piston head 33 in a direction away fromthe coupler head 10 or inwardly of the gear with a progressivelydecreasing external diameter. Such pin, which is in sealed threadedengagement with the secondary piston head as shown, extends through themetering orifice 31 of the piston head and its free end 34 within thepiston is flared to engage the head about the orifice and accordinglylimit the relative extension of the pin. For a purpose to be laterdescribed, the pin is also provided with a through bore 35, with arelief 36 provided in the face of the coupler head 10 which affordscommunication with the pin bore 35 even when the secondary piston is inthe illustrated condition against such coupler face.

The hollow piston is sealed in the cylinder by a main gland preferablyof chevron type and shown as comprising a series of rings 37 of V-shapedcross-section held in compression between machined bronze packing rings38, 39. These rings or chevrons are interleaved with bronze or Teflonspacers 40 to maintain their shape under load, and the compressive loadis applied by a wave spring 41. The assembly is held in place by aretainer washer 42 and a snap ring 43, with positive retention of thelatter assured by machining a recess in the end of the retaining washerand thus making it necessary to physically compress wave spring 41before snap ring 43 can be removed. The gland further includes aconventional wiper and scraper assembly 44 external to the chevron sealunit for removing any foreign material which might adhere to theextended piston, and a grease cavity 45 is incor porated between thechevron unit and the wiper ring to keep the outboard chevrons fromdrying. This is an added precaution to assure long seal life, since ifthe inboard chevrons seal effectively, the remaining rings will be foundto run almost completely dry. It is preferred for this purpose to employa light grease to minimize wear and operating friction, and the cavity45 is fairly large in volume compared to the amount of the grease neededso that servicing at frequent intervals should not be required. The fullassembly is contained in a gland nut 46.

A floating piston 47 is disposed in sealed relation within the hollowpiston 12 to define a variable volume accumulator chamber 48 thereinisolated from the end portion of the piston having communication throughthe metering orifice 31 with the main interior of the cylinder and alsothrough the passages 29 and slots 25 with the annular chamber 49 aboutthat portion of the hollow cylinder which is inboard of the main gland.As will be more fully explained below, the cylinder will be filled withoil, and a charge of pressurized air will be provided in the hollowpiston chamber.

Dual seals are employed for sealing of the floating piston 47, with eachpreferably comprising a standard O-ring 50 in assembly with dualpolytetrafluoroethylene backup rings 51 and a quad ring 52. These quadrings serve not only to preload the O-rings for most efiicient sealing,but also provide two added sealing surfaces and thereby three lines ofcontact instead of the usual single contact in a conventional O-ringinstallation. The backup rings 51 are recommended to insure long life,since they prevent extrusion of the O-ring into the clearance gap duringdynamic operation at high pressures. These backup rings are closelyfitted to both the bore and the O-ring groove, with thepolytetrafluoroethylene selected for long life and minimum friction. Afelt wiper 53 is also used on the air side of the floating piston tomaintain a thin oil film in the piston-accumulator bore, with this alsohelping to enhance long life and leak-free operation.

In addition, the floating piston 47 is provided with one or morepassages 54 which extends from a peripheral relief 55 between the twoseals commonly to an axial passage 56 from which a hollow pilot tube 57extends into the main bore 35 of the metering pin 32. The pilot tube,which is of course movable relative to the pin, has a head 58 at itsfree end sealed to the bore. This tube and passage arrangement providesan atmospheric bleed between the seals completed by vent passage 59 fromthe coupler head relief 36 to the exterior, with the result that fullcharge pressure is always experienced by both to avoid the potentialdifficulty of providing leak-free sealing with essentially zerodifferential pressure.

The gear is also protected against overload, in the event of greaterimpact than normally expected, by a relief valve arrangement mounted onthe piston head 22. This assembly comprises two valve blocks 60 againstthe end face of the head and spaced 180 apart. Each block contains asmall stepped piston 61 controlling a large relief passage 62 extendingto a radial passage 29 and thus in bypass relation to the head meteringorifice 31.

The pistons 61 are loaded by circular spring segments 63 designed toprovide a specific load stroke curve over the required deflection, andthe step dimensions on the pistons are established by the spring loadand by the desired pressure for the relief. The springs 63 will be seennormally to maintain the pistons 61 in extended outward relation, withradial inward movement against the spring load resulting in theuncovering of the relief ports. The latter will be sized to accept thehigh flow rates that will be encountered at impacts in excess of thenormal design value.

This new draft gear is filled and charged in the following manner. Thegland nut 46 is backed off from contact with the cylinder end and asmall air charge is introduced at a fitting 64 in the piston end 13, sothat the accumulator will hold the unit in the neutral position duringfilling. The gland nut has two fill passages 65 closed by plugs 66, andthe latter are removed, with oil supplied through one with the unitvertical and interior air displaced through the other until overflowoccurs, the plugs then being reinstalled. The piston head can beprovided with a plurality of same holes 67 to facilitate the fillingoperation.

The gland nut is then tightened against the cylinder end, and thisaction forces some of the oil through the metering orifice 31 and intothe piston-accumulator, displacing the floating piston 47 from itsoriginal seated position against the primary piston head 22 and slightlycompressing the air charge. This volume of oil serves not only toprevent physical contact of the pistons, but allows for thermalexpansion and contraction during varying ambient temperature conditionsand, moreover, provides a positive reservoir of oil to offset any smallleakage that might occur. Until this excess volume of the oil isdepleted, no amount of leakage will have any effect on the performanceof the gear, and the reservoir volume is designed to be large enough sothat frequent servicing will be unnecessary.

' After this filling and the tightening of the gland nut 46, the unit isthen charged to the full air pressure. However, if desired for handling,the unit can be retracted by reducing the charge and subsequentlyrecharged for extension to the neutral position.

The operation of the gear in buff will now be described. When thecoupler head 10 is struck, the cylinder 11 is forced to the right asshown in the drawings and this will of course be into the car sill. Thecylinder will carry the secondary piston 33 and metering pin 32 in thismovement, while the primary piston 12 and piston head 22 remain fixedrelative to the car. Accordingly, all oil displaced by the motion of thesecondary piston 33 must flow either through the small fixed fillorifices 67 in the piston head 22 or through the central controlledorifice 31. The contour of the metering pin 32 is of course originallyestablished by calculation to provide high efliciency in energyabsorption.

The displaced oil, after passing through the piston head 22, enters theend of the hollow main piston 12 and forces the floating piston 47inwardly to compress the air charge. Part of the oil also flowsoutwardly through the relatively large radial passages 29, therebyforcing open the ring valve 27, so that the flow continues through theslots 25 around the head and increases the volume in the annular cavity49. When the impact has been absorbed or the motion compression stoppedby bottoming of the gland nut 46 against the piston end 13, the airpressure built up in the accumulator will extend the unit to the neutralposition. During this return stroke, the oil flows from cavity 49through the same orifices, but in the opposite direction, and snubbingaction is provided by the ring valve 27 which will be held tightly bythis flow against the bottom of the groove in which it is seated as aresult of its inherent spring action and also the pressure of the oilflowing from the cavity. The orifices 28 in the ring valve are sized toprovide a controlled rate for this return which will preclude any suddenextension causing unwanted reaction forces. This snubbing action in suchproper degree largely eliminates the problems in train dynamics whichcan occur when the train has a number of spring loaded cushioningdevices in series.

It should be noted that the draft gear is designed so that the gland nut46 actually bottoms on the piston end or fitting 13 before any of theinternal parts come into contact. In this manner, the load istransferred directly into the outer cylinder eliminating external bumpstops required by most other cushioning devices. The operation of therelief mechanism has already been described.

With respect to the draft operation, as the coupler is pulled out, itcarries the cylinder 11 with it while the metering pin 32 and secondarypiston 33 are, however, restrained by the primary piston 12 and do notmove relative to the car frame. The volume of oil between the heads ofthe two pistons accordingly does not change, but the volume of annularcavity 49 between the primary piston and the gland nut is reduced. Theonly path for the oil displaced by this reduction is through thesnubbing holes 28 in the ring valve 27, and again this action preventsthe unit from being extended rapidly. At the same time, the air chargepressure acts on the secondary piston area to provide a very highpullout force which may, for example, be on the order of about63,000'lbs. and increase about 2,000 lbs. at full extension because ofthe compression of the charge. At full extension, the primary piston 12bottoms on the gland nut 46, with nominal bearing pressure regardless ofthe large area of contact. As a result of the high pullout force, fullextension would most likely occur only on the forward cars of a trainduring starting or while pulling up grade and under most operatingconditions there will be virtually solid train operation with minimalchange in length.

By way of further illustration, the new design can provide a stroke of13 in buff and 3" in draft, which will be seen to provide over-allperformance superior to conventional end-of-car cushioning devices. Thisunit can provide protection for a car Weighting 222,000 lbs. to at least10 miles per hour, within the standard couplerforce specification of500,000 lbs. when bumped into a car equipped with conventional frictiontype draft gear. The pivotal attachment of the new gear to the car is,

- moreover, shifted inwardly or closer to the truck structure relativeto the usual knuckle and rod type of gear, with such shift clearlyadding to lateral stability by reducing the swing of the coupler head onturning.

I, therefore, particularly point out and distinctly claim as myinvention:

1. In a railroad car draft gear including a cylinder and hollow piston,with a coupler head carried by one and the other adapted to be attachedto the car, a floating piston within the hollow piston, the inner end ofthe latter having an orifice providing communication with the interiorof the hollow piston at one side of the floating piston, the cylinderbeing filled with oil and the hollow piston at the other side of thefloating piston containing compressed air, metering pin means movablerelatively in said orifice to control the area thereof, said meteringpin means having an axial passage, and a pilot member attached to thefloating piston and slidably extending into the passage of the meteringpin means for stabilizing relative movement of the floating position.

2. The combination set forth in claim 1, wherein the metering pin meansis connected to a secondary piston relatively movable within thecylinder and stop means is provided to limit relative retraction of thepin means from the orifice of the hollow piston.

3. The combination set forth in claim 1, wherein the floating pistoncarries two axially spaced seals engaging the interior of the hollowpiston, and passage means extends from the exterior thereof between thetwo seals to an atmospheric vent.

4. The combination set forth in claim 3, wherein the pilot member is atube forming part of said passage means, and the pin means passage isanother part which extends to the atmospheric vent.

5. Railroad car draft gear comprising a cylinder, a

hollow piston, a coupler attached to one of the cylinder and hollowpiston, means for pivotally attaching the other of the cylinder andhollow piston to a railroad car in sill structure of the same, afloating piston within the hollow piston dividing the interior thereofin first and second chambers, an orifice in the hollow piston providingcommunication between the first chamber and the cylinder interior,metering pin means movable relatively in said orifice to vary the areathereof, a secondary piston relatively movable within the cylinder towhich the pin means is attached, and stop means for preventing fullrelative withdrawal of the pin means from the orifice, the first chamberand cylinder being filled with liquid and the second chamber containinga charge of pressurized air which maintains the cylinder and hollowpiston in a neutral partially extended condition.

6. Railroad car draft gear as set forth in claim 5, wherein the hollowpiston has further orifices means therethrough in bypassing relation tothe first-named orifice, and relief valve means applied to the end faceof such hollow piston normally closing said further orifice means andopening the same when the liquid pressure in the cylinder reaches apreselected value, said relief valve means including a valving memberand a curved spring segment biasing the same in the closing direction.

7. Railroad car draft gear as set forth in claim 6, wherein the reliefvalve means comprises a pair of pistons and curved spring segmentsloading the same, said pistons being stepped to provide smalldifferential areas to overcome the spring forces.

8. In a railroad car draft gear including a cylinder and hollow pistonslidable therein, with one carrying a coupler head and the other adaptedfor attachment to the car, a floating piston within the hollow pistonand dividing the interior thereof into first and second chambers, firstorifice means providing communication between the first chamber and thecylinder interior, metermg pin means movable relatively in said orificeto vary the area thereof with relative movement of the cylinder andhollow piston, second orifice means in bypassing relation to the firstorifice means, and relief valve means applied to the end face of thehollow piston and controlling the second orifice means, said reliefvalve means comprising a body forming a continuation passage for thesecond orifice means generally normal to said end face, the passagehaving a side opening, and the valve means further including atraversely movable differential area piston normally closing saidopening and hence the second orifice means, and a curved spring segmentactlng at one end against said differential area piston for loading thesame and being anchored at the other end to the end face of the hollowpiston.

9. Railroad car draft gear comprising a cylinder, a hollow pistonslidable in said cylinder, a coupler head affixed to one of saidcylinder and piston and the other being adapted for attachment to arailroad car, first packing means engaging the inner end portion of thehollow piston and the interior of the cylinder, second packing meansengaging the cylinder adjacent its free end and the exterior of thehollow piston, with the latter formed to provide with the cylinder anannular cavity between the first and second packing means, a floatingpiston movable within the hollow piston to define first and secondchambers of variable volume therein, first and second spaced sealscarried by the floating piston in engagement with the hollow piston,passage means extend- 1ng from the exterior of the floating pistonbetween said first and second seals to an atmospheric vent, first orifice means in the hollow piston providing communication between saidfirst chamber and the cylinder interior, piston-position responsivemeans for controlling the area of said first orifice means, secondorifice means hetween said first chamber and said annular cavity, thecylinder and first chamber being filled with liquid and the secondchamber containing a pressure air charge which maintains the cylinderand hollow piston in a neutral position, and snubbing valve meanscontrolling said second orifice means to provide a controlled lower rateof fiow of the liquid therethrough from the annular cavity to the firstchamber than in the reverse direction.

10. Railroad car draft gear comprising a cylinder, a hollow pistonslidable in said cylinder, a coupler head affixed to one of saidcylinder and piston and the other being adapted for attachment to arailroad car, first packing means engaging the inner end portion of thehollow piston and the interior of the cylinder, second packing meansengaging the cylinder adjacent its free end and the exterior of thehollow piston, with the latter formed to provide with the cylinder anannular cavity between the first and second packing means, a floatingpiston movable within the hollow piston to define first and secondchambers of variable volume therein, first orifice means in the hollowpiston providing communication between said first chamber and thecylinder interior, a metering pin carried by a secondary pistonrelatively movable within the cylinder and through said first orificemeans to control the area thereof, said metering pin having stop meansfor limiting retraction thereof from the first orifice means, secondorifice means between said first chamber and said annular cavity, thecylinder and first chamber being filled with liquid and the secondchamber containing a pressure air charge which maintains the cylinderand hollow piston in a neutral position, and snubbing valve meanscontrolling said second orifice means to provide a controlled lower rateof flow of the liquid therethrough from the annular cavity to the firstchamber than in the reverse direction.

11. Railroad car draft gear as set forth in claim 10, wherein themetering pin has an axially extending passage, and the floating pistonhas a pilot member slidable in said passage.

12. Railroad car draft gear as set forth in claim 11, wherein said pilotmember is a tube and part of passage means extending to the exterior ofthe floating piston, and the pin passage leads to an atmospheric vent.

References Cited DAYTON E. HOFFMAN, Primary Examiner U.S. Cl. X.R.

